U.S. patent number 9,825,473 [Application Number 14/813,733] was granted by the patent office on 2017-11-21 for contactless power transfer system.
This patent grant is currently assigned to Nippon Soken, Inc., Toyota Jidosha Kabushiki Kaisha. The grantee listed for this patent is Nippon Soken, Inc., Toyota Jidosha Kabushiki Kaisha. Invention is credited to Yuji Hayashi, Hiroaki Yuasa.
United States Patent |
9,825,473 |
Hayashi , et al. |
November 21, 2017 |
Contactless power transfer system
Abstract
A power supply ECU controls a converter to have a first control
region in which a voltage is raised as a coupling coefficient is
larger, and a second control region in which the voltage is
maintained at a rating irrespective of a coupling coefficient. An
ECU controls a converter such that an input impedance of the
converter attains a prescribed value in the first control region
and controls the converter such that received electric power
becomes close to a target by changing the input impedance in the
second control region.
Inventors: |
Hayashi; Yuji (Kasugai,
JP), Yuasa; Hiroaki (Miyoshi, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nippon Soken, Inc.
Toyota Jidosha Kabushiki Kaisha |
Nishio-Shi
Toyota-shi, Aichi-ken |
N/A
N/A |
JP
JP |
|
|
Assignee: |
Toyota Jidosha Kabushiki Kaisha
(Toyota-shi, JP)
Nippon Soken, Inc. (Nishio-shi, JP)
|
Family
ID: |
55181019 |
Appl.
No.: |
14/813,733 |
Filed: |
July 30, 2015 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20160036243 A1 |
Feb 4, 2016 |
|
Foreign Application Priority Data
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|
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Aug 4, 2014 [JP] |
|
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2014-158560 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60L
53/38 (20190201); B60L 53/122 (20190201); H02J
50/80 (20160201); H02J 7/025 (20130101); H02J
50/12 (20160201); B60L 53/126 (20190201); H02J
5/005 (20130101); H02J 50/90 (20160201); H02J
7/00034 (20200101); H02J 50/10 (20160201); H02J
5/00 (20130101); Y02T 90/121 (20130101); Y02T
10/7005 (20130101); Y02T 90/12 (20130101); Y02T
90/122 (20130101); Y02T 10/70 (20130101); Y02T
90/125 (20130101); Y02T 90/14 (20130101); Y02T
10/7072 (20130101) |
Current International
Class: |
H02J
5/00 (20160101); H02J 50/80 (20160101); B60L
11/18 (20060101); H02J 7/02 (20160101); H02J
50/10 (20160101) |
References Cited
[Referenced By]
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WO |
|
Primary Examiner: Fureman; Jared
Assistant Examiner: Evans; James
Attorney, Agent or Firm: Dinsmore & Shohl LLP
Claims
What is claimed is:
1. A contactless power transfer system comprising: a power
transmission device; and a power reception device, said power
transmission device including a power transmission unit including a
power transmission coil and a first capacitor connected in series
to said power transmission coil, and configured to transmit
electric power to said power reception device in a contactless
manner, a voltage variable high-frequency power supply configured
to supply alternating-current (AC) power to said power transmission
unit while adjusting a voltage of the voltage variable
high-frequency power supply, and a first control unit controlling
said voltage variable high-frequency power supply, said power
reception device including a power reception unit including a power
reception coil and a second capacitor connected to said power
reception coil, and configured to receive electric power from said
power transmission unit in a contactless manner, an impedance
adjuster provided between said power reception unit and load
equipment, and a second control unit controlling said impedance
adjuster, said first control unit controlling said voltage variable
high-frequency power supply to include a first control region and a
second control region, in the first control region the voltage of
said voltage variable high-frequency power supply being raised as a
coupling coefficient between said power transmission unit and said
power reception unit is larger, a coupling coefficient in the
second control region being larger than that in the first control
region, in the second control region the voltage of said voltage
variable high-frequency power supply being maintained at a constant
value or substantially at said constant value irrespective of said
coupling coefficient, and said second control unit controlling said
impedance adjuster such that an input impedance of said impedance
adjuster becomes equal to a prescribed value or substantially to
said prescribed value when said voltage variable high-frequency
power supply is controlled in said first control region, and
controlling said impedance adjuster such that received electric
power becomes close to a target by changing said input impedance
from said prescribed value or substantially from said prescribed
value when said voltage variable high-frequency power supply is
controlled in said second control region.
2. The contactless power transfer system according to claim 1,
wherein said second capacitor is connected in series to said power
reception coil, and said second control unit controls said
impedance adjuster such that said input impedance becomes greater
than said prescribed value when said voltage variable
high-frequency power supply is controlled in said second control
region.
3. The contactless power transfer system according to claim 1,
wherein said second capacitor is connected in parallel with said
power reception coil, and said second control unit controls said
impedance adjuster such that said input impedance becomes smaller
than said prescribed value when said voltage variable
high-frequency power supply is controlled in said second control
region.
4. The contactless power transfer system according to claim 1,
wherein said power reception device further includes a rectifier
configured to rectify AC power received by said power reception
unit, and said impedance adjuster is a first converter provided
between said rectifier and said load equipment.
5. The contactless power transfer system according to claim 1,
wherein said prescribed value is set based on a rated current of
said power reception device.
6. The contactless power transfer system according to claim 1,
wherein said prescribed value is set at an input impedance at which
maximum transfer efficiency is implemented when said coupling
coefficient is a prescribed minimum value.
7. The contactless power transfer system according to claim 1,
wherein said voltage variable high-frequency power supply includes
an inverter connected to said power transmission unit, and a second
converter configured to adjust an input voltage of said inverter,
said first control unit controls said second converter such that
said input voltage is raised as said coupling coefficient is larger
in said first control region, and controls said second converter
such that said input voltage is maintained at a rated voltage of
said inverter or substantially at said rated voltage thereof
irrespective of said coupling coefficient in said second control
region, the voltage of said voltage variable high-frequency power
supply is the input voltage of said inverter, and said first
control unit maintains the voltage of said voltage variable
high-frequency power supply at said constant value or substantially
at said constant value by maintaining said input voltage at said
rated voltage or substantially at said rated voltage.
Description
This nonprovisional application is based on Japanese Patent
Application No. 2014-158560 filed on Aug. 4, 2014, with the Japan
Patent Office, the entire contents of which are hereby incorporated
by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a contactless power transfer
system for transferring electric power from a power transmission
device to a power reception device in a contactless manner.
Description of the Background Art
Japanese Patent Laying-Open No. 2013-215066 discloses a power
transfer system for transferring electric power from a power
transmission device to a power reception device in a contactless
manner. In this power transfer system, the power reception device
includes a power receiving-side resonator, a rectifier, a DC/DC
converter, and a control device. Based on the input voltage of the
DC/DC converter, the control device calculates a current command
value at which the input impedance of the DC/DC converter is set at
a set value, and then, controls the DC/DC converter such that the
input current of the DC/DC converter becomes equal to the current
command value.
According to this power transfer system, since the input impedance
of the DC/DC converter is maintained constant during the operation
period of the DC/DC converter, input impedance matching can always
be achieved, so that power transfer efficiency can be improved (see
Japanese Patent Laying-Open No. 2013-215066).
In the above-described power transfer system, the magnitude of the
coupling coefficient between the power transmission device and the
power reception device is not taken into consideration. In the case
where the DC/DC converter is controlled so as to have an input
impedance kept constant, if the coupling coefficient is relatively
small, the power transmission voltage needs to be lowered in the
power transmission device in order to ensure the desired power
reception current (the input current of the DC/DC converter). In
the case where prescribed electric power is transferred from the
power transmission device to the power reception device, when a
voltage is lowered in the power transmission device, the flowing
current is increased. Consequently, loss is increased, so that the
efficiency may entirely decrease.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-described
problems. An object of the present invention is to provide a
contactless power transfer system for transferring electric power
from a power transmission device to a power reception device for
the purpose of suppressing deterioration of the efficiency of the
entire system when the coupling coefficient is relatively
small.
According to the present invention, the contactless power transfer
system includes a power transmission device and a power reception
device. The power transmission device includes a power transmission
unit, a voltage variable high-frequency power supply, and a first
control unit. The power transmission unit includes a power
transmission coil and a first capacitor connected in series to the
power transmission coil, and is configured to transmit electric
power to the power reception device in a contactless manner. The
voltage variable high-frequency power supply is configured to
supply alternating-current (AC) power to the power transmission
unit while adjusting a voltage of the voltage variable
high-frequency power supply. The first control unit controls the
voltage variable high-frequency power supply. The power reception
device includes a power reception unit, an impedance adjuster, and
a second control unit. The power reception unit includes a power
reception coil and a second capacitor connected to the power
reception coil, and is configured to receive electric power from
the power transmission unit in a contactless manner. The impedance
adjuster is provided between the power reception unit and load
equipment. The second control unit controls the impedance adjuster.
The first control unit controls the voltage variable high-frequency
power supply to include: a first control region in which a voltage
of the voltage variable high-frequency power supply is raised as a
coupling coefficient between the power transmission unit and the
power reception unit is larger; and a second control region that is
larger in coupling coefficient than the first control region and in
which the voltage of the voltage variable high-frequency power
supply is maintained at a constant value or substantially at the
constant value irrespective of the coupling coefficient. The second
control unit controls the impedance adjuster such that an input
impedance of the impedance adjuster becomes equal to a prescribed
value or substantially to the prescribed value when the voltage
variable high-frequency power supply is controlled in the first
control region, and controls the impedance adjuster such that
received electric power becomes close to a target by changing the
input impedance from the prescribed value or substantially from the
prescribed value when the voltage variable high-frequency power
supply is controlled in the second control region.
According to this contactless power transfer system, in the first
control region, the larger the coupling coefficient is, the higher
the voltage of the voltage variable high-frequency power supply is
set. In the second control region, the voltage of the voltage
variable high-frequency power supply is maintained at a constant
value or substantially at the constant value irrespective of the
coupling coefficient. Therefore, in the second control region, the
received electric power can be controlled to be a target by
changing the input impedance of the impedance adjuster from the
prescribed value or substantially from the prescribed value. By
providing such a second control region, the minimum voltage of the
voltage variable high-frequency power supply in the first control
region can be raised as compared with the case where the input
impedance is always controlled to be constant. By raising the
voltage of the voltage variable high-frequency power supply, the
flowing current is suppressed, so that loss is suppressed.
Therefore, according to this contactless power transfer system, it
becomes possible to suppress deterioration of the efficiency of the
entire system when the coupling coefficient is relatively
small.
Preferably, the second capacitor is connected in series to the
power reception coil. The second control unit controls the
impedance adjuster such that the input impedance of the impedance
adjuster becomes greater than the prescribed value when the voltage
variable high-frequency power supply is controlled in the second
control region.
In the configuration in which the second capacitor is connected in
series to the power reception coil, the impedance adjuster is
controlled in the second control region such that the input
impedance of the impedance adjuster becomes greater than the
prescribed value, so that the minimum voltage of the voltage
variable high-frequency power supply in the first control region
can be raised while ensuring the desired received electric power in
the power reception device. Therefore, according to this
contactless power transfer system, it becomes possible to suppress
deterioration of the efficiency of the entire system when the
coupling coefficient is relatively small.
Furthermore, preferably, the second capacitor is connected in
parallel with the power reception coil. The second control unit
controls the impedance adjuster such that the input impedance of
the impedance adjuster becomes smaller than the prescribed value
when the voltage variable high-frequency power supply is controlled
in the second control region.
In the configuration in which the second capacitor is connected in
parallel with the power reception coil, the impedance adjuster is
controlled in the second control region such that the input
impedance of the impedance adjuster becomes smaller than the
prescribed value, so that the minimum voltage of the voltage
variable high-frequency power supply in the first control region
can be raised while ensuring the desired received electric power in
the power reception device. Therefore, according to this
contactless power transfer system, it becomes possible to suppress
deterioration of the efficiency of the entire system when the
coupling coefficient is relatively small.
Preferably, the power reception device further includes a rectifier
configured to rectify AC power received by the power reception
unit. The impedance adjuster is a first converter provided between
the rectifier and the load equipment.
In this contactless power transfer system, the converter provided
between the rectifier and the load equipment is employed as an
impedance adjuster. Accordingly, the impedance adjuster does not
have to be provided separately from the converter. Therefore, this
contactless power transfer system can suppress the increase in
number of devices mounted in the power reception device.
Preferably, the prescribed value is set based on a rated current of
the power reception device.
By providing such a configuration, it becomes possible to suppress
deterioration of the efficiency of the entire system at a
relatively small coupling coefficient while suppressing the current
received by the power reception device to be equal to or less than
the rated current.
Furthermore, preferably, the prescribed value is set at an input
impedance at which maximum transfer efficiency is implemented when
the coupling coefficient is a prescribed minimum value.
By providing such a configuration, the input impedance can be
changed appropriately in accordance with the change in the coupling
coefficient while maintaining high transfer efficiency.
Preferably, the voltage variable high-frequency power supply
includes an inverter connected to the power transmission unit and a
second converter configured to adjust an input voltage of the
inverter. The first control unit controls the second converter such
that the inverter input voltage is raised as the coupling
coefficient is larger in the first control region, and controls the
second converter such that the inverter input voltage is maintained
at a rated voltage of the inverter or substantially at the rated
voltage thereof irrespective of the coupling coefficient in the
second control region. The voltage of the voltage variable
high-frequency power supply is the input voltage of the inverter.
The first control unit maintains the voltage of the voltage
variable high-frequency power supply at the constant value or
substantially at the constant value by maintaining the inverter
input voltage at the rated voltage of the inverter or substantially
at the rated voltage thereof.
By providing such a configuration, the inverter input voltage in
the first control region can be raised as compared with the case
where the input impedance is always controlled to be constant. The
inverter input voltage is raised, so that loss in the inverter is
suppressed. Therefore, according to this contactless power transfer
system, it becomes possible to suppress deterioration of the
efficiency of the entire system when the coupling coefficient is
relatively small.
The foregoing and other objects, features, aspects and advantages
of the present invention will become more apparent from the
following detailed description of the present invention when taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an entire configuration diagram of a contactless power
transfer system according to the first embodiment of the present
invention.
FIG. 2 is a diagram showing the circuit configuration of a power
transmission unit and a power reception unit shown in FIG. 1.
FIG. 3 is a diagram showing an example of the circuit configuration
of a converter shown in FIG. 1.
FIG. 4 is a diagram showing the relation between the coupling
coefficient and the voltage in the power transmission device.
FIG. 5 is a diagram showing the relation between the coupling
coefficient and the equivalent resistance of a load that receives
received electric power.
FIG. 6 is a diagram showing the relation between the equivalent
resistance and the transfer efficiency from the power transmission
unit to the power reception unit.
FIG. 7 is a functional block diagram of a power supply ECU shown in
FIG. 1.
FIG. 8 is a control block diagram of an ECU shown in FIG. 1.
FIG. 9 is a control block diagram of a control unit shown in FIG.
8.
FIG. 10 is a flowchart for illustrating a process procedure of
external charging control carried out by the ECU.
FIG. 11 is a flowchart for illustrating the process procedure of a
power supply ECU during external charging control.
FIG. 12 is a diagram showing the circuit configuration of a power
transmission unit and a power reception unit in the second
embodiment.
FIG. 13 is a diagram showing the relation between the coupling
coefficient and the voltage of the power transmission device in the
second embodiment.
FIG. 14 is a diagram showing the relation between the coupling
coefficient and the equivalent resistance in the second
embodiment.
FIG. 15 is a diagram showing the relation between the equivalent
resistance and the transfer efficiency from the power transmission
unit to the power reception unit.
FIG. 16 is a control block diagram of a control unit of an ECU in
the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention will be hereinafter
described in detail with reference to the accompanying drawings, in
which the same or corresponding components are designated by the
same reference characters, and description thereof will not be
repeated.
First Embodiment
(Configuration of Contactless Power Transfer System)
FIG. 1 is an entire configuration diagram of a contactless power
transfer system according to the first embodiment of the present
invention. Referring to FIG. 1, the contactless power transfer
system includes a power transmission device 100 and a power
reception device 200 that is mounted in a vehicle. Power
transmission device 100 is provided external to the vehicle, and
can charge a power storage device 140 mounted in the vehicle
(charging of power storage device 140 in the vehicle by power
transmission device 100 provided external to the vehicle will also
be hereinafter referred to as "external charging").
Power transmission device 100 includes a rectifier 10, a voltage
variable high-frequency power supply 15, a power transmission unit
40, a power supply ECU (Electronic Control Unit) 50, a voltage
sensor 60, and a communication device 70. Rectifier 10 rectifies AC
power received from an external power supply 80 such as a
commercial system power supply, and outputs the rectified power to
voltage variable high-frequency power supply 15. In the case where
external power supply 80 is a DC (direct-current) power supply,
rectifier 10 does not have to be provided.
Voltage variable high-frequency power supply 15 generates AC power
having a prescribed transmission frequency, adjusts the voltage of
the generated AC power, and outputs the adjusted voltage to power
transmission unit 40. By way of example, in the contactless power
transfer system according to the present first embodiment, voltage
variable high-frequency power supply 15 includes a converter 20 and
an inverter 30.
Converter 20 is provided between rectifier 10 and inverter 30, and
adjusts the voltage supplied to inverter 30 (an input voltage of
inverter 30) based on a control signal PWC1 received from power
supply ECU 50. Converter 20 is formed of a boost chopper circuit,
for example.
Inverter 30 is connected between converter 20 and power
transmission unit 40. Inverter 30 converts the DC power obtained by
voltage adjustment by converter 20 into AC power having a
prescribed transmission frequency, and supplies the converted AC
power to power transmission unit 40. Inverter 30 is formed of a
single-phase full bridge circuit, for example. Voltage sensor 60
detects the voltage adjusted by converter 20, that is, a voltage
Vin supplied to inverter 30, and outputs the detected value to
power supply ECU 50.
Power transmission unit 40 includes a resonance circuit (a coil and
a capacitor) for transmitting electric power to power reception
unit 110 of power reception device 200 in a contactless manner.
When power transmission unit 40 receives AC power having a
transmission frequency from inverter 30, it generates an
electromagnetic field around power transmission unit 40. Power
transmission unit 40 transmits electric power through the generated
electromagnetic field to power reception unit 110 of power
reception device 200 in a contactless manner. The specific
configuration of power transmission unit 40 will be described later
together with power reception unit 110.
Power supply ECU 50 includes a CPU, a storage device, an
input/output buffer, and the like (each of which is not shown), and
performs various types of control in power transmission device 100.
As main control of power supply ECU 50 according to the present
invention, during execution of external charging by power
transmission device 100, power supply ECU 50 generates control
signal PWC1 for adjusting voltage Vin by converter 20 and outputs
the generated control signal PWC1 to converter 20. Specific control
for converter 20 associated with external charging will be
described later in detail.
Furthermore, power supply ECU 50 determines whether voltage Vin
detected by voltage sensor 60 has reached a rated voltage (the
upper limit voltage) of inverter 30 or not, and controls
communication device 70 to transmit the determination result to
power reception device 200. The detected value of voltage Vin may
be transmitted to power reception device 200 by means of
communication device 70, and it may be determined in power
reception device 200 whether voltage Vin has reached the rated
voltage or not.
On the other hand, power reception device 200 includes a power
storage device (load equipment) 140, a power reception unit 110, a
rectifier 120, a converter 130, and an ECU 150. Furthermore, power
reception device 200 includes voltage sensors 160, 162, current
sensors 164, 166, and a communication device 170.
Power reception unit 110 includes a resonance circuit (a coil and a
capacitor) for receiving electric power from power transmission
unit 40 of power transmission device 100 in a contactless manner.
Power reception unit 110 receives electric power from power
transmission unit 40 in a contactless manner through the
electromagnetic field generated around power transmission unit 40.
Power reception unit 110 is disposed, for example, in the lower
part of the vehicle body located relatively close to the front side
thereof, and receives electric power from power transmission unit
40 that is disposed on the surface of the ground or in the
ground.
Rectifier 120 rectifies the AC power received by power reception
unit 110 and outputs the rectified power to converter 130.
Converter 130 is provided between rectifier 120 and power storage
device 140 corresponding to load equipment, and adjusts the input
impedance of converter 130 based on a control signal PWC2 received
from ECU 150. Specifically, converter 130 adjusts the input
impedance by adjusting a voltage Vc input into converter 130. This
adjustment of the input impedance by converter 130 will be
described later in detail.
Power storage device 140 is a rechargeable DC power supply and is
configured of a secondary battery such as a lithium-ion battery or
a nickel-metal hydride battery, for example. Power storage device
140 is charged by receiving electric power received by power
reception unit 110. The electric power stored in power storage
device 140 is supplied to a vehicle drive device, auxiliary
machinery and the like that are not shown. In addition, power
storage device 140 may be configured by a power storage element
such as an electric double layer capacitor in place of a secondary
battery.
Voltage sensor 160 detects voltage Vc input into converter 130, and
outputs the detected value to ECU 150. Current sensor 164 detects a
current Ic input into converter 130, and outputs the detected value
to ECU 150. Voltage sensor 162 detects the output voltage of
converter 130, that is, a voltage Vb of power storage device 140,
and outputs the detected value to ECU 150. Current sensor 166
detects the current supplied from converter 130 to the power
storage device, that is, a current Ib showing the charging current
for power storage device 140, and outputs the detected value to ECU
150.
ECU 150 includes a CPU, a storage device, an input/output buffer,
and the like (each of which is not shown), and performs various
types of control in power reception device 200. As main control of
ECU 150 according to the present invention, ECU 150 performs
external charging control for carrying out external charging for
the purpose of charging power storage device 140 by means of power
transmission device 100. During execution of external charging
control, ECU 150 generates control signal PWC2 for adjusting the
input impedance of converter 130, and outputs the generated control
signal PWC2 to converter 130. Furthermore, ECU 150 determines
whether charge power Pout of power storage device 140 has reached a
charge power command value Pout* or not, and controls communication
device 170 to transmit the determination result to power
transmission device 100. The details of external charging control
will be described later.
FIG. 2 is a diagram showing the circuit configuration of power
transmission unit 40 and power reception unit 110 shown in FIG. 1.
Referring to FIG. 2, power transmission unit 40 includes a coil 42
and a capacitor 44. Capacitor 44 is connected in series to coil 42
and forms a resonance circuit together with coil 102. Capacitor 44
is provided for adjusting the resonance frequency of power
transmission unit 40. Power reception unit 110 includes a coil 112
and a capacitor 114. Capacitor 114 is connected in series to coil
112 and forms a resonance circuit together with coil 112. Capacitor
114 is provided for adjusting the resonance frequency of power
reception unit 110. Power transmission unit 40 and power reception
unit 110 are designed to resonate each other in transmission
frequency of the electric power transmitted from power transmission
unit 40 to power reception unit 110. It is preferable that a Q
factor showing the resonance strength of power transmission unit 40
and power reception unit 110 is equal to or greater than 100.
FIG. 3 is a diagram showing an example of the circuit configuration
of converter 20 shown in FIG. 1. Converter 130 of power reception
device 200 also has the circuit configuration similar to that of
converter 20. Referring to FIG. 3, converter 20 includes a
capacitor 21, a coil 22, a switching element 23, a diode 24
connected in anti-parallel to switching element 23, and a diode 25.
Each of these elements forms a boost chopper circuit. The duty
ratio of switching element 23 is controlled by power supply ECU 50
(FIG. 1). Converter 20 can adjust the voltage between terminals T7
and T8 to be equal to or greater than the voltage between terminals
T5 and T6 in accordance with the duty ratio of switching element
23.
(Description of External Charging Control)
Again referring to FIG. 1, in this contactless power transfer
system, during execution of external charging, converter 20 is
controlled in power transmission device 100 and converter 130 is
controlled in power reception device 200 such that charge power
Pout of power storage device 140 becomes equal to desired charge
power command value Pout*.
In this case, in accordance with the parking position of the
vehicle relative to power transmission device 100, the relative
positional relation between power transmission unit 40 of power
transmission device 100 and power reception unit 110 of power
reception device 200 changes, and a coupling coefficient k between
power transmission unit 40 and power reception unit 110 changes. In
the contactless power transfer system according to the present
first embodiment, external charging control is carried out
differently between the first control region in which coupling
coefficient k is relatively small and the second control region in
which coupling coefficient k is relatively large, which will be
hereinafter described.
In the contactless power transfer system according to the present
first embodiment, the so-called "SS (Series-Series) system"
configuration is employed, in which capacitor 44 is connected in
series to coil 42 in power transmission unit 40 while capacitor 114
is connected in series to coil 112 also in power reception unit
110, as shown in FIG. 2. Such an SS system circuit has immittance
characteristics, in which case a current Iout of power reception
unit 110 is proportional to the voltage of power transmission unit
40. Furthermore, under the condition that the electric power
transmitted from power transmission unit 40 to power reception unit
110 is controlled to be constant, voltage Vout of power reception
unit 110 is increased as coupling coefficient k between power
transmission unit 40 and power reception unit 110 is larger.
Accordingly, current Iout of power reception unit 110 is decreased.
As the magnitude of the voltage on power transmission unit 40 is
adjusted in accordance with voltage Vin, the following relation
lies among current Iout of power reception unit 110, voltage Vin
adjusted in power transmission device 100 and coupling coefficient
k based on the above description. Iout=.alpha.1(Vin/k) (1)
In this case, .alpha.1 is a constant. As apparent from the equation
(1), when coupling coefficient k is relatively small, voltage Vin
needs to be lowered in power transmission device 100 in order to
obtain desired current Iout in power reception unit 110. On the
other hand, when coupling coefficient k is relatively large,
voltage Vin needs to be raised. However, the upper limit (rated
voltage) determined by the breakdown voltage and the like of each
element is set for voltage Vin. Accordingly, when voltage Vin is
suppressed to the rated voltage even though coupling coefficient k
is relatively large, desired current Iout may not be achieved.
FIG. 4 is a diagram showing the relation between coupling
coefficient k and voltage Vin in power transmission device 100.
Furthermore, FIG. 5 is a diagram showing the relation between
coupling coefficient k and an equivalent resistance RL of the load
that receives the received electric power. It is to be noted that
the equivalent resistance is an impedance of the load formed of
power storage device 140 and converter 130 of power reception
device 200, and corresponds to the input impedance of converter
130. Equivalent resistance RL can be detected based on the input
voltage and the input current of converter 130, and is adjusted by
controlling converter 130.
Referring to FIGS. 4 and 5, solid lines show voltage Vin and
equivalent resistance RL, respectively, in the contactless power
transfer system according to the present first embodiment, while
dotted lines show voltage Vin and equivalent resistance RL,
respectively, in the conventional system as a reference example.
First described will be the concept of the conventional setting of
voltage Vin and equivalent resistance RL.
Conventionally, equivalent resistance RL is adjusted to a
prescribed value RLini without taking coupling coefficient k into
consideration (FIG. 5). As described above, when voltage Vin is
suppressed to a rated voltage Vr in the case where coupling
coefficient k is relatively large, desired current Iout may not be
achieved. Conventionally, voltage Vin attains rated voltage Vr when
coupling coefficient k is at the maximum (the power reception unit
is located opposite to the power transmission unit), and voltage
Vin is lowered as coupling coefficient k becomes smaller (the
dotted line in FIG. 4). However, according to such setting of
voltage Vin, voltage Vin is lowered when coupling coefficient k is
relatively small, with the result that the current flowing through
the power transmission device is increased, thereby increasing
loss.
Thus, in the contactless power transfer system according to the
present first embodiment, voltage Vin is raised as compared with
the conventional case (the solid line in FIG. 4). When voltage Vin
is raised, voltage Vin may reach rated voltage Vr in a range in
which coupling coefficient k is smaller than maximum value kmax.
When voltage Vin is limited to rated voltage Vr, current Iout
lowers in the region where coupling coefficient k is relatively
large, as apparent from the equation (1). Accordingly, in this
first embodiment, in the region (R2) having coupling coefficient k
at which voltage Vin reaches rated voltage Vr, equivalent
resistance RL is adjusted by converter 130 such that equivalent
resistance RL is increased as coupling coefficient k is larger
(FIG. 5). Specifically, charge power Pout is expressed by
Iout.sup.2.times.RL. Accordingly, desired charge power Pout is
ensured by increasing equivalent resistance RL in accordance with
the decrease in current Iout by suppressing voltage Vin to rated
voltage Vr. By providing such a configuration, voltage Vin can be
raised in power transmission device 100 while achieving charge
power Pout as indicated by charge power command value Pout*.
Consequently, loss in power transmission device 100 can be
reduced.
In addition, in the region (R1) having coupling coefficient k at
which voltage Vin can be raised in accordance with coupling
coefficient k, equivalent resistance RL is set at prescribed value
RLini. This prescribed value RLini can be determined, for example,
based on a rated current Ioutr of current Iout in power reception
unit 110 by the following equation. RLini=Pout*/Ioutr.sup.2 (2)
By employing this prescribed value RLini, current Iout exceeding
rated current Ioutr can be prevented from flowing into power
reception unit 110.
Alternatively, prescribed value RLini may be determined based on
equivalent resistance RL at which the maximum transfer efficiency
is implemented at the time when coupling coefficient k attains a
prescribed minimum value kmin.
FIG. 6 is a diagram showing the relation between equivalent
resistance RL and transfer efficiency .eta. from power transmission
unit 40 to power reception unit 110. Referring to FIG. 6, the
larger coupling coefficient k is, the more transfer efficiency
.eta. is increased. Furthermore, the larger coupling coefficient k
is, the more equivalent resistance RL allowing implementation of
the maximum transfer efficiency .eta. is increased. Thus, as shown
in FIG. 5, in the contactless power transfer system according to
this first embodiment, in consideration of the fact that equivalent
resistance RL is increased as coupling coefficient k is larger in
region R2, equivalent resistance RL allowing implementation of the
maximum transfer efficiency when coupling coefficient k attains
prescribed minimum value kmin is set at prescribed value RLini. In
this case, in region R2, equivalent resistance RL can be changed
such that equivalent resistance RL becomes larger than prescribed
value RLini as coupling coefficient k is larger.
Again referring to FIG. 1, function sharing between ECU 150 and
power supply ECU 50 during external charging control will be
hereinafter described. Charge power Pout supplied to power storage
device 140 is managed in ECU 150 based on voltage Vb and current
Ib. At the beginning of start of external charging, ECU 150 sends a
power-transmission command to power supply ECU 50 such that charge
power Pout becomes equal to charge power command value Pout*. Power
supply ECU 50 controls converter 20 based on the power-transmission
command, and converter 20 adjusts voltage Vin. In other words,
power supply ECU 50 controls voltage Vin such that charge power
Pout becomes equal to charge power command value Pout*. On the
power reception device 200 side, ECU 150 controls converter 130
such that equivalent resistance RL (the input impedance of
converter 130) attains prescribed value RLini or substantially
prescribed value RLini. The expression of "substantially prescribed
value RLini" means a value obtained at the time when the impedance
varies inevitably in the case where equivalent resistance RL is
controlled to be maintained at "prescribed value RLini".
If coupling coefficient k between power transmission unit 40 and
power reception unit 110 is relatively small, charge power Pout is
controlled by converter 20 variably controlling voltage Vin in
power transmission device 100. On the other hand, if coupling
coefficient k is relatively large, voltage Vin is to reach rated
voltage Vr. When voltage Vin has reached rated voltage Vr, power
supply ECU 50 controls converter 130 to maintain voltage Vin at
rated voltage Vr, and also notifies ECU 150 that voltage Vin has
reached rated voltage Vr.
When ECU 150 receives the notification from power transmission
device 100 that voltage Vin has reached rated voltage Vr in power
transmission device 100, it controls converter 130 in the direction
in which equivalent resistance RL is increased such that charge
power Pout becomes equal to charge power command value Pout*.
Specifically, when voltage Vin is saturated in power transmission
device 100 due to a relatively large coupling coefficient k, ECU
150 then comes to take charge of controlling charge power Pout.
Then, ECU 150 adjusts equivalent resistance RL to thereby control
charge power Pout.
In control region R1 in which coupling coefficient k is relatively
small, thus, in power transmission device 100, voltage Vin of
inverter 30 is controlled by converter 20 to be increased as
coupling coefficient k is larger; and in power reception device
200, equivalent resistance RL is maintained by converter 130 at
prescribed value RLini or substantially at prescribed value
RLini.
In control region R2 that is larger in coupling coefficient k than
control region R1, on the other hand, in power transmission device
100, voltage Vin is maintained at rated voltage Vr or substantially
at rated voltage Vr; and in power reception device 200, equivalent
resistance RL is adjusted to a value greater than prescribed value
RLini by converter 130. By providing such a configuration, the
minimum value of voltage Vin in power transmission device 100 can
be raised as compared with the conventional case, and the current
flowing through power transmission device 100 is reduced so that
loss can be suppressed.
In this case, the term "substantially at rated voltage Vr" means a
value obtained when voltage Vin varies inevitably even when this
voltage Vin is controlled to be maintained at rated voltage Vr.
Although an explanation has been given in the above description
with regard to the example focusing on the input voltage of
inverter 30 as an example of the "voltage of the voltage variable
high-frequency power supply", the "voltage of the voltage variable
high-frequency power supply" may for example be an output voltage
of inverter 30 or may be an output voltage of converter 20.
FIG. 7 is a functional block diagram of power supply ECU 50 shown
in FIG. 1. Referring to FIG. 7, power supply ECU 50 includes a
converter control unit 52 and a communication unit 54. Converter
control unit 52 receives information about a deviation .DELTA.P of
the charge power (the difference with charge power command value
Pout*) through communication unit 54 from power reception device
200. This information may be the value itself of deviation .DELTA.P
or may be the symbol or the like of deviation .DELTA.P.
Then, converter control unit 52 generates control signal PWC1 for
adjusting voltage Vin to reduce deviation .DELTA.P based on the
information about deviation .DELTA.P, and outputs the generated
control signal PWC1 to converter 20. Furthermore, when voltage Vin
detected by voltage sensor 60 reaches rated voltage Vr, converter
control unit 52 notifies power reception device 200 through
communication unit 54 that voltage Vin has reached rated voltage
Vr.
FIG. 8 is a control block diagram of ECU 150 shown in FIG. 1.
Referring to FIG. 8, ECU 150 includes a charge power calculation
unit 152, an equivalent resistance calculation unit 154, a control
unit 156, and a communication unit 158.
Charge power calculation unit 152 calculates charge power Pout of
power storage device 140 based on the detected value of each of
voltage Vb and current Ib, and outputs the calculated value to
control unit 156. Equivalent resistance calculation unit 154
calculates equivalent resistance RL (the input impedance of
converter 130) by dividing the detected value of voltage Vc by the
detected value of current Ic, and outputs the calculated value to
control unit 156.
Control unit 156 calculates deviation .DELTA.P between charge power
command value Pout* and charge power Pout, and transmits the
information about deviation .DELTA.P to power transmission device
100 by means of communication unit 158. Furthermore, control unit
156 receives the voltage information of power transmission device
100 from power transmission device 100 by means of communication
unit 158. This voltage information includes the information showing
whether voltage Vin has reached rated voltage Vr or not in power
transmission device 100. Then, control unit 156 generates control
signal PWC2 for controlling converter 130 based on charge power
Pout and its command value Pout*, equivalent resistance RL and its
prescribed value RLini, and the voltage information about voltage
Vin from power transmission device 100.
FIG. 9 is a control block diagram of control unit 156 shown in FIG.
8. Referring to FIG. 9, a subtraction unit 212 subtracts charge
power Pout (actual value) from charge power command value Pout*,
and outputs the calculation result to a PI control unit 214 as
.DELTA.P. PI control unit 214 performs proportional and integral
calculation using deviation .DELTA.P calculated by subtraction unit
212 as an input, and outputs the calculation result to an addition
unit 216 as a correction amount .DELTA.RL of the equivalent
resistance.
Addition unit 216 adds correction amount .DELTA.RL to a prescribed
value RLini of the equivalent resistance, and outputs the
calculation result to multiplexer 218. Multiplexer 218 receives the
output of addition unit 216 and prescribed value RLini each as an
input, and receives a signal RA as a selection signal. Signal RA is
a signal received from power transmission device 100 and showing
the voltage information about voltage Vin. Also, this signal RA is
activated when voltage Vin reaches rated voltage Vr. When signal RA
is deactivated, multiplexer 218 outputs prescribed value RLini as
an equivalent resistance command value RL*. When signal RA is
activated, multiplexer 218 outputs the output of addition unit 216,
that is, the value obtained by adding correction amount .DELTA.RL
to prescribed value RLini, as equivalent resistance command value
RL*.
Subtraction unit 220 subtracts equivalent resistance RL (actual
value) from equivalent resistance command value RL*, and outputs
the calculation result to a PI control unit 222 as .DELTA.RL. PI
control unit 222 performs proportional and integral calculation
using deviation .DELTA.RL calculated by subtraction unit 220 as an
input, and outputs the calculation result to a duty calculation
unit 224. Duty calculation unit 224 generates signal PWC2 for
controlling converter 130 based on the output of PI control unit
222.
FIG. 10 is a flowchart for illustrating a process procedure of
external charging control carried out by ECU 150. The process shown
in the flowchart is called from a main routine, while external
charging is requested, for a certain time period or every time a
prescribed condition is satisfied, and then executed.
Referring to FIG. 10, ECU 150 acquires each detected value of
voltage sensors 160, 162 and current sensors 164, 166 during
execution of external charging (step S10). Then, ECU 150 calculates
equivalent resistance RL (actual value) based on each detected
value of voltage Vc and current Ic on the input side of converter
130 (step S20). It is to be noted that this equivalent resistance
RL is calculated by dividing the detected value of voltage Vc by
the detected value of current Ic.
Then, ECU 150 calculates charge power Pout (actual value) based on
each detected value of voltage Vb and current Ib (step S30). Then,
ECU 150 determines whether or not deviation .DELTA.P between charge
power command value Pout* and charge power Pout is larger than a
threshold value .DELTA.Pth (step S40). When deviation .DELTA.P is
equal to or smaller than threshold value .DELTA.Pth (No in step
S40), ECU 150 causes the process to proceed to step S110 without
carrying out a series of subsequent processes.
When it is determined in step S40 that deviation .DELTA.P is larger
than threshold value .DELTA.Pth (YES in step S40), ECU 150
transmits the information about deviation .DELTA.P to power
transmission device 100 by communication device 170 (step S50).
Furthermore, based on the voltage information about voltage Vin (at
least including the information about whether voltage Vin has
reached rated voltage Vr in power transmission device 100) received
from power transmission device 100, ECU 150 determines whether
coupling coefficient k is included in first control region R1 or in
second control region R2 (FIGS. 4 and 5) (step S60).
When voltage Vin has not reached rated voltage Vr and it is
determined that coupling coefficient k is included in first control
region R1 (the region in which coupling coefficient k is relatively
small) (YES in step S70), ECU 150 sets equivalent resistance
command value RL* at prescribed value RLini (step S80). On the
other hand, when voltage Vin has reached rated voltage Vr and it is
determined that coupling coefficient k is included in second
control region R2 (the region in which coupling coefficient k is
relatively large) (NO in step S70), ECU 150 changes equivalent
resistance command value RL* from prescribed value RLini based on
charge power Pout (increases equivalent resistance command value
RL* in accordance with deviation .DELTA.P) as illustrated in FIG. 9
(step S90).
Then, when equivalent resistance command value RL* is calculated in
step S80 or S90, ECU 150 controls converter 130 such that
equivalent resistance PL (the input impedance of converter 130)
becomes equal to equivalent resistance command value RL* (step
S100).
FIG. 11 is a flowchart for illustrating the process procedure of
power supply ECU 50 during external charging control. The process
shown in the flowchart is also called from a main routine, while
external charging is requested, for a certain time period or every
time a prescribed condition is satisfied, and then executed.
Referring to FIG. 11, power supply ECU 50 determines whether the
information about deviation .DELTA.P between charge power command
value Pout* and charge power Pout has been received or not from
power reception device 200 (step S210). When it is determined that
the information about .DELTA.P has not been received (NO in step
S210), power supply ECU 50 causes the process to proceed to step
S270 without carrying out a series of subsequent processes.
When it is determined in step S210 that the information about
.DELTA.P has been received (YES in step S210), power supply ECU 50
receives the detected value of voltage Vin that is an input voltage
of inverter 30 (step S220). Then, power supply ECU 50 determines
whether voltage Vin has reached rated voltage Vr or not (step
S230).
When it is determined that voltage Vin has not reached rated
voltage Vr (NO in step S230), power supply ECU 50 carries out
voltage variable control for adjusting voltage Vin based on
deviation .DELTA.P of the charge power received from power
reception device 200 (step S240). It is to be noted that voltage
Vin may be increased or decreased in accordance not with the value
itself of deviation .DELTA.P but with the symbol of deviation
.DELTA.P.
On the other hand, when it is determined in step S230 that voltage
Vin has reached rated voltage Vr (YES in step S230), power supply
ECU 50 carries out voltage fixing control for maintaining voltage
Vin at rated voltage Vr (step S250). Then, power supply ECU 50
transmits, to power reception device 200, the voltage information
at least including the information about whether voltage Vin has
reached rated voltage Vr or not (step S260).
As described above, in this first embodiment, by dividing external
charging control into first control region R1 and second control
region R2 in which voltage Vin is maintained at a rating as
described above, the minimum voltage of voltage variable
high-frequency power supply 15 (the minimum value of voltage Vin)
can be raised, as compared with the case where the input impedance
of converter 130 is always controlled to be constant. By raising
the voltage of voltage variable high-frequency power supply 15, the
flowing current is suppressed, thereby suppressing loss. Therefore,
according to this first embodiment, it becomes possible to suppress
deterioration of the efficiency of the entire system when coupling
coefficient k is relatively small.
Furthermore, in the present first embodiment, converter 130 is
utilized as an impedance adjuster by adjusting the boosting ratio
and the duty of converter 130 provided between rectifier 120 and
power storage device 140. Thereby, the increase in number of
components mounted in power reception device 200 is suppressed, but
the impedance adjuster is not limited to converter 130. For
example, a circuit including a capacitor and a coil may be provided
separately from converter 130 between power storage device 140 and
power reception unit 110. Also, this circuit may be used for
adjusting the impedance.
Second Embodiment
This second embodiment is different in circuit configuration of the
power reception unit from the above-described first embodiment.
Accordingly, this second embodiment is different from the first
embodiment in the method of adjusting the equivalent resistance
(input impedance) on the vehicle side at the time when voltage Vin
has reached rated voltage Vr in power transmission device 100.
The entire configuration of the contactless power transfer system
according to the present second embodiment is the same as that in
the contactless power transfer system according to the first
embodiment shown in FIG. 1.
FIG. 12 is a diagram showing the circuit configuration of a power
transmission unit 40 and a power reception unit 110# in the second
embodiment. Referring to FIG. 12, the circuit configuration of
power transmission unit 40 is the same as the configuration of the
first embodiment shown in FIG. 2. Power reception unit 110#
includes a coil 112 and a capacitor 116. Capacitor 116 is connected
in parallel with coil 112 and forms a resonance circuit together
with coil 112. Capacitor 116 is provided in order to adjust the
resonance frequency of power reception unit 110#. Then, power
transmission unit 40 and power reception unit 110# are designed to
resonate each other in the transmission frequency of the electric
power transmitted from power transmission unit 40 to power
reception unit 110. It is preferable that a Q factor showing the
resonance strength of power transmission unit 40 and power
reception unit 110# is equal to or greater than 100.
In the contactless power transfer system according to the present
second embodiment, the so-called the "SP (Series-Parallel) system"
configuration is employed, in which capacitor 44 is connected in
series to coil 42 in power transmission unit 40 while capacitor 116
is connected in parallel with coil 112 in power reception unit
110#. Such an SP system circuit has ideal transformer
characteristics, and serves as a voltage source to a load (the
voltage on power reception unit 110# is proportional to the voltage
on power transmission unit 40). The following relation lies among
voltage Vout of power reception unit 110#, voltage Vin adjusted in
power transmission device 100, and coupling coefficient k.
Vout=.alpha.2(Vin/k) (3)
In this case, .alpha.2 is a constant. As apparent from the equation
(3), when coupling coefficient k is relatively small, voltage Vin
needs to be lowered in power transmission device 100 in order to
achieve desired voltage Vout in power reception unit 110#. On the
other hand, when coupling coefficient k is relatively large,
voltage Vin needs to be raised. However, voltage Vin cannot be
raised above rated voltage Vr. If voltage Vin is suppressed to the
rated voltage even though coupling coefficient k is relatively
large, desired voltage Vout may not be able to be achieved.
FIG. 13 is a diagram showing the relation between coupling
coefficient k and voltage Vin of power transmission device 100 in
the second embodiment. FIG. 14 is a diagram showing the relation
between coupling coefficient k and equivalent resistance RL in the
second embodiment. Referring to FIGS. 13 and 14, solid lines show
voltage Vin and equivalent resistance RL, respectively, in the
contactless power transfer system according to the present second
embodiment, while dotted lines show voltage Vin and equivalent
resistance RL, respectively, in the conventional system as a
reference example.
As in the conventional case (dotted line), if equivalent resistance
RL is adjusted to prescribed value RLini without taking coupling
coefficient k into consideration (FIG. 14) and voltage Vin is set
so as to attain rated voltage Vr when coupling coefficient k is at
the maximum, voltage Vin lowers when coupling coefficient k is
relatively small, with the result that the flowing current is
increased to thereby increase loss.
Accordingly, also in the contactless power transfer system
according to the present second embodiment, as in the first
embodiment, voltage Vin is increased as compared with the
conventional case (the solid line in FIG. 13). Then, voltage Vin
can reach rated voltage Vr in a range in which coupling coefficient
k is smaller than maximum value kmax. When voltage Vin is limited
to rated voltage Vr, voltage Vout lowers in a region where coupling
coefficient k is relatively large as apparent from the equation
(3). Thus, according to this second embodiment, in second control
region R2 where voltage Vin reaches rated voltage Vr, equivalent
resistance RL is adjusted by converter 130 such that equivalent
resistance RL is decreased as coupling coefficient k is larger
(FIG. 14). Specifically, as charge power Pout is expressed by
Vout.sup.2/RL, equivalent resistance RL is lowered in accordance
with the decrease in voltage Vout by suppressing voltage Vin to
rated voltage Vr, thereby ensuring desired charge power Pout. By
providing such a configuration, voltage Vin can be raised in power
transmission device 100 while achieving charge power Pout as
indicated by charge power command value Pout*. Consequently, loss
in power transmission device 100 can be reduced.
In addition, in this second embodiment, prescribed value RLini of
equivalent resistance RL can be determined, for example, based on a
lower limit voltage Vbmin of power storage device 140 by the
following equation. RLini=Vbmin.sup.2/Pout* (4)
Furthermore, minimum value RLmin of equivalent resistance RL
obtained when coupling coefficient k reaches maximum value kmax can
be determined, for example, based on rated current Ioutr of current
Iout in power reception unit 110# by the following equation.
RLmin=Pout*/Ioutr.sup.2 (5)
By adjusting equivalent resistance RL in this way, current Iout
exceeding rated current Ioutr can be prevented from flowing into
power reception unit 110#.
In addition, prescribed value RLini may be determined based on
equivalent resistance RL at which the maximum transfer efficiency
is implemented at the time when coupling coefficient k reaches
maximum value kmax.
FIG. 15 is a diagram showing the relation between equivalent
resistance RL and transfer efficiency .eta. from power transmission
unit 40 to power reception unit 110#. Referring to FIG. 15, also in
the SP system, transfer efficiency .eta. is increased as coupling
coefficient k is larger. On the other hand, in the SP system,
equivalent resistance RL allowing implementation of maximum
transfer efficiency .eta. is decreased as coupling coefficient k is
larger. Thus, as shown in FIG. 14, in the contactless power
transfer system according to this second embodiment, in
consideration of the fact that equivalent resistance RL is
decreased as coupling coefficient k is larger in region R2,
equivalent resistance RL allowing implementation of the maximum
transfer efficiency when coupling coefficient k reaches maximum
value kmax is set at prescribed value RLini. In this case, in
region R2, equivalent resistance RL can be changed such that
equivalent resistance RL is decreased below prescribed value RLini
as coupling coefficient k is larger.
The configuration of power supply ECU 50 in the second embodiment
is the same as that in the first embodiment shown in FIG. 7.
Furthermore, the entire configuration of ECU 150 in the second
embodiment is also the same as that in the first embodiment shown
in FIG. 8.
FIG. 16 is a control block diagram of a control unit 156# of ECU
150 in the second embodiment. Referring to FIG. 16, control unit
156# includes a subtraction unit 217 in place of addition unit 216
in the configuration of control unit 156 in the first embodiment
shown in FIG. 9. Subtraction unit 217 subtracts a correction amount
.DELTA.RL of the equivalent resistance, which is output from PI
control unit 214, from prescribed value RLini of the equivalent
resistance, and outputs the calculation result to multiplexer 218.
Then, when signal RA is activated, multiplexer 218 outputs the
output of subtraction unit 217, that is, the value obtained by
subtracting correction amount .DELTA.RL from prescribed value
RLini, as equivalent resistance command value RL*. Accordingly,
adjustment to equivalent resistance RL shown in FIG. 14 can be
achieved.
As described above, also in the present second embodiment of the SP
system, it becomes possible to suppress deterioration of the
efficiency of the entire system when coupling coefficient k is
relatively small, as in the case of the first embodiment employing
the SS system.
In the above description, power supply ECU 50 corresponds to one
embodiment of the "first control unit" in the present invention,
and ECU 150 corresponds to one embodiment of the "second control
unit" in the present invention. Furthermore, converter 130
corresponds to one embodiment of each of the "impedance adjuster"
and the "first converter" in the present invention, and converter
20 corresponds to one embodiment of the "second converter" in the
present invention.
Each embodiment disclosed herein is also intended to be combined as
appropriate and thereby implemented. It should be understood that
the embodiments disclosed herein are illustrative and
non-restrictive in every respect. The scope of the present
invention is defined by the terms of the claims, and is intended to
include any modifications within the meaning and scope equivalent
to the terms of the claims.
* * * * *